ISO 361
Encyclopedia
International standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
that specifies the shape, proportions, application and restrictions on the use of the symbol.
It may be used to signify the actual or potential presence of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
. The standard does not specify the radiation levels at which it is to be used.